Paclitaxel is a well known chemotherapeutic drug for treatment of various metastatic cancers. It has been approved by FDA and HPB for the treatment of ovarian and breast cancers.
The compound is a natural product, primarily extracted from the bark of the Pacific yew tree, Taxus brevifolia, and is also found in T. baccata, T. walichiana, T. yunnanensis and T. canadensis.
The concentration of paclitaxel in various raw materials is typically low, for example, on the order of between 0.0004 and 0.01% (w/w) in the bark of Pacific yew. Such low concentration render the extraction and purification of the compound to pharmaceutical grade from raw materials very challenging, and heretofore impractical on a commercial scale. Various normal phase chromatography and reverse phase chromatography as well as low and high pressure column chromatography techniques have been developed to purify paclitaxel from a crude extract of raw material.
The success of low pressure chromatography greatly depends on the nature of the column. Various problems are associated with the use of silica gel and alumina trioxide, all of which are classical supports of the stationary phase in partition systems. They form a stable stationary phase with most solvent systems, but it is a strong absorbent and may participate in the separation process to the extent that chromatographic behaviour and recovery of samples are affected.
Chromatographic methods have been developed to detect and isolate paclitaxel from various Taxus species on analytical and preparative basis. These isolation processes are mainly conducted on a small laboratory scale and suffer from low selectivity, recovery and high production cost, thereby presenting a serious and unfulfilled need for an economically practicable method for separating the valuable anti-tumor compound paclitaxel from its close analog cephalomanine as well as other closely related taxanes.
Prior art methods disclose the use of various types of chromatographic techniques to separate paclitaxel and related taxanes, including normal phase and reverse phase chromatography on a silica gel or bonded silica gel column. The prior art methods are end up at low yield, high production cost or involved multiple separation steps which were difficult to scale up to large industrial scale production.
Characteristic of the prior art is U.S. Pat. No. 5,620,875, issued Apr. 15, 1997, to Hoffman et al. The document teaches the separation of paclitaxel and other taxanes by multiple step hexane extractions and high performance liquid chromatography (HPLC). The process is involved, labor intensive and only provides moderate yields of the desired compounds.
In U.S. Pat. No. 5,670,673, issued Sep. 23, 1997, to Rao, the isolation and purification of Taxol and its analogues is delineated. The process includes the use of reverse phase liquid chromatography on a C18 adsorbent with elution of the adsorbed analogues. Although a meritorious procedure, limitations exist with this technique in terms of productivity and purity of compounds obtained.
The present invention provides a simple separation method based on a polymeric resin column which is devoid the limitations of the existing methodology.